From Fuel to Smoke: Composition of a Flame from a Prescribed Fire and its Near-Field Plume
ALLA ZELENYUK, Schuyler Lockwood, Zezhen Cheng, Tracy Baker, Ashley Bradley, Kendall Hughey, Joey Chong, Stephen Baker, Emily Lincoln, Shawn Urbanski, David Lignell, Zisimos Toumasatos, Georgios Karavalakis, David Weise, Timothy Johnson, Pacific Northwest National Laboratory
Abstract Number: 573
Working Group: Combustion
Abstract
Predicting smoke emissions is important for modeling the spread and energy release of a wildland fire. Though emissions higher up in smoke plumes have been studied, the composition and chemical processes in the flame itself (both at and above the fuel source) that directly influence the plume emissions are not well-understood.
Recently we conducted over 50 controlled burns of longleaf pine needle beds to characterize in real-time the evolution of gas-phase effluents and aerosol particles emitted by the flame as a function of height above the fuel bed. The gases were primarily analyzed using a Fourier transform infrared spectrometer, while aerosol particles were characterized using a single particle mass spectrometer, miniSPLAT, condensation particle counter, and Engine Exhaust Particle Sizer. Three fixed heights (20 cm, 50 cm, and 80 cm above the fuel bed) were established to facilitate the measurements of the persistent (pyrolysis), intermittent (flame), and plume (smoke) phases of effluents in and above the flame, respectively.
Preliminary results show that gas-phase products were dominated primarily by CO2 in the plume and flame regions, while CO, CH4, C2H2 and C2H4 are significant contributors in the fuel zone. Particle properties, including their number concentrations, size distributions, compositions and morphology were also shown to vary greatly by zone. Particles in plume and intermittent zones were dominated by fractal agglomerates of primary spherules dominated by elemental carbon, while particles in the persistent zone comprised of a mixture of spherical particles and agglomerates with higher effective densities and contained high fractions of organics (i.e., polyaromatic hydrocarbons). Finally, particle number concentrations decreased significantly with the height above the fuel bed.
These findings suggest the physicochemical characteristics of the emissions are not uniform with respect to the height above the fuel, and these differences need to be accounted for in modeling of fire dynamics.